LIM kinase 1 acts as a profibrotic mediator in permanent atrial fibrillation patients with valvular heart disease.

Atrial fibrillation (AF) is the most frequently diagnosed cardiac arrhythmia worldwide. Patients with permanent atrial fibrillation are at an increased risk of developing valvular heart disease. Atrial fibrosis occurs in this pathophysiological setting. LIM kinase 1 (LIMK1) is a serine/threonine kinase that regulates microtubule stability and actin polymerization in fibroblasts. LIMK1 has been implicated in the pathogenesis of atrial fibrillation. Clinical data and biopsies of the right atrial appendage were collected from 50 patients with valvular heart disease who underwent heart valve replacement surgery. Data from patients with permanent atrial fibrillation (AF) and patients with sinus rhythm (SR) were compared. We found that AF patients had upregulated expression of LIMK1 as well as higher fibrosis. Transforming growth factor-β (TGF-β) stimulation induced the differentiation of cardiac fibroblasts into myofibroblasts as well as upregulated expression of LIMK1. Downregulation of LIMK1 by siRNA inhibited TGF-β induced fibroblast-myofibroblast transition, as evidenced by the downregulation of the expression of several differentiation markers, namely alpha-smooth muscle actin and type I and III collagen. Our findings revealed that increased LIMK1 protein levels may contribute to atrial fibrosis, and suggested that LIMK1 might be involved in AF development by promoting fibrogenesis associated with TGF-β.